Cotton mill dust, cotton plant parts (trash), and synthetic dusts were treated with gaseous agents. Endotoxin (LPS) content was reduced in cotton mill dust by vapor phase treatments. Vaporous agents included ammonia, ethylene oxide, and, trifluoroacetic acid. Each agent was effective in lowering LPS content but the amount of reduction was dependent on initial concentration. Some samples were screened by the Ames test. No Ames test mutagenic activity was found in the cotton dust samples or its extracts as screened.